The project is related to the isolation of proforms of fibrous elastin from lung tissue. A fibrous elastin precursor which is approximately 70,000 daltons in size has been isolated from the lung tissue of the copper-deficient chick. This protein is similar in property to tropoelastin which has been isolated from the aortas of copper-deficient swine and chicks. In addition, a protein, which has an amino acid composition similar to tropoelastin (i.e., eighty-five percent of the total residues as gly, ala, val, pro and over 40 residues/1000 residues lys), has also been isolated with an apparent molecular weight of 130,000 daltons. The protein appears to be a proform of tropoelastin. Selective isolation of the "proelastin" is achieved by precipitation with NaCl (19 to 15% w/v) after removal of collagen by acid precipitation. Studies are currently being conducted to establish more clearly a precursor-product relationship with respect to the putative proform and tropoelastin and their roles in the final formation of fibrous elastin. BIBLIOGRAPHIC REFERENCES: R.B. Rucker and K. Tom (1976) Arterial Elastin. Am. J. Clin. Nutr. 29: 1021-1034. R. B. Rucker and D. Tinker (1977) Elastin structure and metabolism. In: International Review of Experimental Pathology (Will appear in Vol. 17, March or April).